1. Field of the Invention
The present invention relates to a wireless LAN, and more particularly, to a method and apparatus for measuring a channel in a wireless LAN system.
2. Related Art
Recently, with the development of an information communication technology, various wireless communication technologies have been developed. Among the wireless communication technologies, a wireless local area network (WLAN) is a technology to wirelessly access to an Internet in a home, a company, or a specific service providing area by using portable terminals such as a personal digital assistant (PDA), a laptop computer, and a portable multimedia player (PMP) based on a wireless frequency technology.
In order to overcome a limit to a communication speed which has been pointed out as vulnerability in the WLAN, as a relatively recently established technical standard, there is the institute of electrical and electronics engineers (IEEE) 802.11n. The IEEE 802.11n is to increase a speed and reliability of a network and extend an operating distance of a wireless network. In more detail, the IEEE 802.11n supports a high throughout (HT) of which a data processing speed is maximally 540 Mbps or more. Further, in order to minimize a transmission error and optimize a data speed, the IEEE 802.11n is based on a multiple-input and multiple-output (MIMO) technology using a multi antenna for both a transmitting unit and a receiving unit.
As distribution of the WLAN has been activated and applications using the WLAN have been diversified, recently, the need for a new WLAN system for supporting a higher throughput than a data processing speed supported by the IEEE 802.11n A next-generation WLAN system supporting a very high throughput (VHT), as a next version of the IEEE 802.11n WLAN system, is one of the IEEE 802.11n WLAN systems which has been recently newly proposed in order to support a data processing speed of 1 Gbps or more in a media access control (MAC) service access point (SAP).
The next-generation WLAN system supports a multi user (MU)-MIMO transmission in which a plurality of non-AP stations (STA) simultaneously accesses a channel in order to effectively use a wireless channel. According to the MU-MIMO transmission mode, the AP may simultaneously transmit a frame to one or more STA which are MIMO paired.
In order to perform the MU-MIMO transmission, there is a need to accurately effectively measure a channel of each user.